A typical data storage system stores and retrieves data on behalf of one or more external hosts. One conventional data storage system includes multiple front-end director circuits, multiple back-end director circuits, cache memory, and disk drives. The director circuits (or simply directors) reside on circuit boards, e.g., four directors per director circuit board. Similarly, the cache memory resides on circuit boards, e.g., a fixed number of megabytes (MB) of high-speed volatile memory per memory circuit board.
The directors move data into and out of the cache memory. In particular, the front-end directors operate as interfaces between the external hosts and the cache memory by moving data between the hosts and the cache memory. Similarly, the back-end directors operate as interfaces between the cache memory and the disk drives by moving data between the cache memory and the disk drives.
In one version of the above-described conventional data storage system, the director circuit boards and the memory circuit boards connect to a backplane interconnect that provides four multi-drop buses. The directors access the cache memory by coordinating use of the four multi-drop buses. Since there exists four multi-drop buses, different directors can simultaneously use different buses thus achieving higher bandwidth. Furthermore, each director has access to each of the multi-drop buses for fault tolerance purposes, i.e., there is another bus available if one particular bus fails.
In another version of the above-described conventional data storage system, the director circuit boards and the memory circuit boards connect to a backplane interconnect that provides a point-to-point communications pathway between each director circuit board and each memory circuit board. The point-to-point communications pathways between the director circuit boards and the memory circuit boards alleviate bus contention issues (e.g., delays in waiting for an available bus), thus reducing communications latencies between directors and the cache memory. Additionally, multiple pathways exist from each front-end director to the disk drives, through the cache memory and the back-end directors, thus providing for higher bandwidth and fault tolerance.